The field of the invention pertains to electronic apparatus which transmits signals into the sea, and electronically responds to the echo signals to visually display fish, vegetation and structure causing the echo signals.
Echo ranging apparatus to aid fishermen in locating fish in the sea has long been of interest to fishermen.
Traditionally, this involves a transmitter, which transmits pulsed bursts to a transducer which converts these bursts of electrical energy to bursts of ultrasonic energy transmitted by the sea. Typically, the echo signals are then reconverted to electrical energy (by the same or a different transducer) and electronically treated, including amplification, to determine through a varying voltage level, a visual display of the fish, vegetation and structure (including the sea bed) causing the echoes.
This type of system has been and is presently being used, but has left fishermen with much to be desired. In particular, the visual display (which is typically accomplished by electrochemical paper which converts voltage levels to degrees of lightness and darkness) presents difficulties at distinguishing between the sea bed and fish near or along the sea bed where they commonly are, or fish among vegetation.
To address this, several approaches have been attempted with some degree of success. According to one approach, exemplified by Sparling et al, U.S. Pat. No. 3,098,210, apparatus is connected between stages which carry out the amplification function to cause a blanking (essentially a terminating) of the signal presented to the electrochemical paper when the signal reaches a predetermined level, e.g., corresponding to the strong signal of the sea bed. This approach results in the loss of information during such blanking, after the echo from the sea bed or the echo from other matter (e.g., fish) which may cause such blanking. The blanking is typically for a time interval which is substantially less than the time it takes to receive the echoes from a signal pulse (and to print a corresponding line along the paper). However, the blanking, upon its initiation, can be maintained until after the echo signals from the pulse have terminated (and the line has been printed). This latter approach may result in the loss of information over a relatively long interval following the initiation of any blanking. The former approach may result in successive losses of information due to successive instances of blanking along a printout line.
Another approach in effect provides three set output levels, dependent upon the range in which the levels of the echo signals fall. It is apparent that this limitation to three discrete levels also results in the sacrifice of substantial information.
The present invention substantially advances the art of echo ranging apparatus by displaying a continuum of variations resulting from variations in the levels of the echo signals, both before a high triggering level is reached and after the triggering, by reducing the levels after such triggering while preserving information-carrying variations.